/**
 * @param {character[]} s
 * @return {void} Do not return anything, modify s in-place instead.
 */
 var reverseString = function(s) {
  let i = 0;
  let j = s.length - 1;
  while(i < j) {
    let A = s[i];
    let B = s[j];
    s[i] = B;
    s[j] = A;
    i++;
    j--;
  }
  return s;
};
console.log(reverseString(["H","a","n","n","a","h"]))